A DIMM or dual in-line memory module comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers. DIMMs began to replace SIMMs as the predominant type of memory module as Intel P5-based Pentium processors began to gain market share.
While the contacts on SIMMs on both sides are redundant, DIMMs have separate electrical contacts on each side of the module. Another difference is that standard SIMMs have a 32-bit data path, while standard DIMMs have a 64-bit data path. Since Intel's Pentium many processors have a 64-bit bus width, requiring SIMMs installed in matched pairs in order to populate the data bus. The processor would then access the two SIMMs in parallel. DIMMs were introduced to eliminate this practice.
The most common types of DIMMs are:
⁕72-pin SO-DIMM, used for FPM DRAM and EDO DRAM
⁕100-pin DIMM, used for printer SDRAM
⁕144-pin SO-DIMM, used for SDR SDRAM
⁕168-pin DIMM, used for SDR SDRAM
⁕172-pin MicroDIMM, used for DDR SDRAM